Unable to select Custom Supervisor Type in checklist task Owner

Hi Team,

We have a Requirement to add Custom Supervisor Type in checklist task Owner, so we can trigger notification to the supervisor type.

for Example: we have supervisor type called HRG for one of our customers. the requirement is when a line Manager (Performer) completes his/her Checklist task then the notification should go to HRG (Owner). but we can see the options from the dropdown are Line Manager, Initiator, AOR and Specific Person and Not option to choose custom supervisor type.

please let us know if there any work around.